Fluids of various kinds may be administered to a body by means of a hollow needle in conjunction with a source of the required fluid. For example, such a needle may be associated with a syringe holding a liquid drug, the needle being used to penetrate the body at the site at which the drug is to be administered. Equally, body fluids may be withdrawn by using a hollow needle which is used to penetrate the body until the tip is located at the site from which fluid is to be withdrawn.
A recognised hazard for clinicians and other persons using or handling medical needles for the above described purposes is the risk of a so-called needle-stick injury—that is to say the accidental penetration of another's skin by the needle. Prior to the use of the needle to supply a fluid to or to withdraw fluid from a body, this rarely presents much of a problem, though once the needle has been used, there is a very much higher risk of a serious consequence for the clinician, or others associated with the disposal of a used needle. During use of the needle to penetrate the body tissues of a patient, the needle is likely to become contaminated with various organisms; should someone subsequently suffer a needle-stick injury, infection could occur.
There have been numerous proposals for protecting the sharp tip of a used needle, in order to reduce the risk of a needle-stick injury following use of the needle. Some proposals have actually increased the likelihood of such an injury by virtue of the action which must be performed to protect the tip, even if the risk thereafter is lessened. Despite all of the proposals which have previously been made, very few have achieved commercial success, nor has there been wide acceptance by the medical industry. Many proposals are somewhat complex and involve a significantly greater manufacturing cost, and so are unacceptable on economic grounds. Others are much more difficult to use as compared to an unprotected needle, and so are rejected by clinicians. Yet further proposals do not allow compliance with best practice protocols.
A device which protects a needle tip after use without an operator having to perform any extra step on withdrawing the needle from a body is usually referred to as a passive protection device. This may be contrasted with an active protection device, where an operator is required to perform an extra step in order to protect a needle, following the withdrawal of the needle from a body. The requirement to perform an extra step leaves the needle unprotected for a longer period than with a passive protection device and further the performance of that extra step exposes the operator to a potentially hazardous situation, when needle-stick accidents can occur.
There is a significant demand for a passive protection device for use with a needle and which allows a clinician or perhaps others to use the needle in much the same way as is done with an unprotected needle, but which can be manufactured economically and which provides a high degree of protection against needle-stick injury. In the case of health professionals, this demand is driven by health and safety legislation but in the case of others performing self-injections using a so-called pen injector, the used needles must be disposed of safely with minimum risk to others, even in the event that a sharps container is not immediately available. Further, particularly for self-injections, it is highly preferred that the device operates fully automatically, without intervention by the user, so as wholly to prevent access to the needle tip both before and after use, other than by a determined attempt to override the protection. In this way, protection may be afforded not just to the clinician or other user of the needle, but also to people who could come into a risky situation with used needles, such as waste disposal operators, cleaners, and so on.
Passive protection devices mostly have used metal helical coil springs to urge a protecting sleeve forwardly to a protecting position over a needle, but this in general adds to the cost of a device, which is of course a throw-away item, once used. The cost may be reduced by moulding an integral plastics material spring with a component of the device, but this leads to difficulties associated with creep of plastics materials stored when stressed. These can be alleviated to some extent by using leaf springs running on surfaces inclined to the needle axis. Early designs can be found in U.S. Pat. Nos. 4,553,541, 5,421,347 and US 2002/0087180. A more recent development, directed to protecting an injection needle, is described in EP1558311 (Salvus Technology).
Another such device has been described in WO2011/092518 (Liversidge). This provides a simple, easy to use and economically viable safety device, conferring passive protection to the needle. The device of WO2011/092518 may be moulded from plastics materials and does not require the use of metal springs, as the device addresses the known problem of a plastic spring in that if the spring is stored in a stressed condition, there is a likelihood that the spring will lose at least some of its resilience and so may not be able to return to its as-manufactured unstressed condition. Though the device of WO2011/092518 incorporates a plastic spring, it is designed to be stored with the spring in a substantially unstressed condition but is able to operate effectively and reliably, to give passive needle-stick protection.
It is a feature of the device of WO2011/092518 that as soon as the needle shielding sleeve has been moved through a small distance from its needle shielding position, release of the sleeve will result in the device locking-out, so preventing subsequent movement of the sleeve from its needle protecting position. It is however sometimes highly advantageous for a user of the device to be able to move the sleeve to expose the sharp tip of the needle before actually performing an medical procedure, for example for aspirating the syringe to which the needle is attached, or perhaps for drawing a drug into the syringe. Such action is not possible with the device of WO2011/092518.